Dock levelers are used to transfer goods between a building and a truck trailer. They bridge the gap between the building floor to the bed of the trailer or similar carrier. Levelers include a frame or support structure to mount it in a pit of a loading dock. The rear end of the leveler is hinged to the building floor. The opposite end of the leveler has an extendable lip plate that engages the trailer bed. A doorway is positioned over the loading dock and its pit. The doorway is opened to load and unload a trailer, and closed when the dock stall is not in use. Conventional levelers are designed to store in either a horizontal or vertical position. Horizontally stored levelers are adapted to move from a generally horizontal position where the upper surface of the deck is flush with the surface of the building floor to a second generally inclined position to provide a ramp between the bed of the truck and the dock floor. When stored in the pit, the door seals against the top of the loading dock deck. The door does not extend to the bottom of the pit. Hot or cold air, humidity, dust and insects can enter the building via the pit. Vertically stored levelers are adapted to move from a generally vertical stored position to a generally inclined position to provide a ramp between the bed of the truck trailer and the dock floor. When stored, these levelers are located entirely inside the building so that the overhead door can seal off the pit to seal the interior of the building from thermal losses, humidity, dust, insects, etc. Vertically stored levelers are particularly suited for docks handling food and other refrigerated goods.
Various mechanisms have been developed for extending and retracting the lip of a dock leveler during operation. Two common types are pivotally extending the lip and telescopically extending the lip. When the lip extends pivotally, the lip extends from its pendant stored position to its extended position when the ramp is raised or when the operator walks the ramp down. Examples of pivotally extended lips are disclosed in U.S. Pat. No. 3,137,017 to Pfleger, U.S. Pat. No. 3,997,932 to Artzberger, U.S. Pat. No. 4,398,315 to Driear, U.S. Pat. No. 5,475,888 to Massey, and U.S. Pat. Nos. 6,834,409 and 7,013,519 to Gleason, the disclosures of which are incorporated by reference. When the lip extends telescopically, the lip extends from its stored position under the deck of the leveler to its extended position. Examples of telescopically extended lips are disclosed in U.S. Pat. Nos. 5,001,799 and 5,396,676 to Alexander, U.S. Pat. No. 5,450,643 to Warner and U.S. Pat. No. 5,586,355 to Metz, the disclosures of which are incorporated by reference.
Conventional vertically stored levelers have a hinged lip. The lip fully extends to rest on a trailer bed when loading or unloading a trailer. When extended, the lip is flush with and relatively parallel to the deck of the leveler. When cargo has been loaded or unloaded, the deck is raised to remove the lip from the trailer. As the deck rises, the lip moves to a pendent position so that when the deck is vertically stored, the lip is roughly perpendicular to the deck.
A problem with conventional vertically stored dock levelers is end loading a trailer. The lip is extended up to two feet into the trailer. Cargo cannot be placed at the end of the trailer without setting the cargo on the lip of the leveler. Placing cargo on the lip inhibits raising the leveler to remove the lip from the trailer. Thus, to end load the trailer, the deck must be raised and lowered so that the lip hangs pendent to fit in a gap between end of the dock floor and the trailer bed as shown in FIG. 14. This extra step takes time. A worker must park and get off a forklift to operate the dock leveler. The deck has to be raised, and pneumatic cylinders must discharge to allow the hinged lip to hang pendent. Then the deck has to be lowered to a position that brings its front end even with the trailer bed. These additional steps reduce dock efficiency. They also cause additional wear and tear on the leveler, which increases the frequency of routine maintenance. If a dock worker does not wait for the lip to hang entirely pendent, the tip of the lip can strike, gouge or otherwise damage the trailer. In addition, when unloading an already end loaded trailer, the lip cannot be extended to bridge the gap between the trailer bed and dock floor. The cargo at the end of the trailer prevents the deployment of the lip. The cargo at the end of the trailer must first be unloaded without the use of the lip. The leveler is then raised and lowered to deploy the lip into the trailer to further unload the trailer.
Another problem with conventional vertically stored dock levelers during end loading is that the pendent lip does not bridge the gap between the trailer bed and dock floor. The exposed gap can allow a forklift wheel to inadvertently be driven or slip into this gap. Cargo can fall off the forklift and be damaged, and the time needed to lift the forklift out of the gap reduces dock efficiency. The exposed gap also poses a potential safety concern for dock workers who can inadvertently trip on or step into this gap. Goods, tools and other items can also fall through the gap to further reduce dock efficiency. Moving the lip to a pendant position also frequently interferes with the operation of the vehicle restraint securing the trailer to the loading dock. The restraint frequently needs to be disengaged to allow the lip to hang pendent. Disengaging the vehicle restraint allows inadvertent and unsafe movement of the truck while workers are still end loading the trailer.
A further problem with vertically stored levelers is controlling the movement of the deck relative to the movement of the hinged lip. The leveler must clear the overhead door. The deck should not be raised to its vertical position until the hinged lip moves to its pendent position. The total height of the leveler must be shorter than the height of the door opening. The total height of a vertically stored leveler with the lip extended can exceed 9 to 12 feet, which can exceed the height of the door opening, or impact ventilation ducts, piping, wiring, or other components in the interior of the loading dock. Although loading dock doors are designed to accommodate vertically stored levelers when the lip is pendent, they may not accommodate the leveler when its lip is extended. A leveler with an extended lip can strike and damage the overhead door or the components in the interior of the dock.
A still further problem with conventional dock levelers is keeping the controls and the wiring for the controls as simple as possible. Complicated control system wiring is difficult to install, and can result in installation and maintenance errors. Components that have to be wired a particular way are more complicated, and can lead to wires being inadvertently crossed.
A still further problem with conventional dock levelers is the use of limit switches to control the raising and lowering of the deck. The limit switches are typically placed at or near the perimeter of the doorway, which is an inherently busy area of a loading dock. The switches can be inadvertently bumped and result in a leveler malfunction.
The present invention is intended to solve these and other problems.